Recovery of secondary olefins from acid extracts



Patented Sept. 10, 1946 RECOVERY OF SECONDARY OLEFINS FROM ACID EXTBACTSHarold W. Scheeline, Elizabeth, J., assignor to Standard Oil DevelopmentCompany, a corporation of Delaware Application February 14, 1942, SerialNo. 430,872

3 Claims. (01. 260-677) I This invention relates to improvements in theseparation and recovery of secondary olefins from mixtures of olefinsand saturated hydrocarbons which are associated in gaseous and lightliquid hydrocarbon mixtures and more particularly the separation ofolefins having from itself (e. g. isobutane) and (2) difficulty in re- 3to 5 carbon atoms to the molecule from mixcovering the desired productafter pyrolysis. tures of hydrocarbons or mixtures consisting Pureolefinic hydrocarbons have been sepamainly of olefins and saturatedhydrocarbons. rated from naphthas containing the olefins di- Theseparation of olefins by fractional distillae' luted with paraffinichydrocarbons of approxition from saturated hydrocarbons having themately the same boiling point by treating the same number of carbonatoms to the molecule, naphtha with sulfuric acid under such conditionsas in the case of mixtures produced by cracking of acid strength,temperature, etc., as to selecor pyrolysis of petroleum oils or otherbituminous tively extract the olefins into the acid phase. materials, isvery diiiicult. In most cases, it is The acid extract containing olefinsmay then be impossible for all practical purposes, for example,subjected to conditions whereby the olefin is reto fractionally separateby distillation propylene covered and the acid returned to theextraction boiling at 48.2 C. from propane which boils at steph has endone heretofore by S a e 45.0 C. The separation of 4 carbon atomoledilution with water followed by steam stripping. fins and saturatedhydrocarbons that are found It is W611 known that Sulfuric acid y a y ina cracked hydrocarbon mixture is still more poiymeriZe the olefins andvis Well known that, difiicult, as ey a e ore numerous and have theolefin-sulfuric acid reaction products the following boiling points: areheated without sufficient dilution, polymer- Bomng Points 0 C izationand secondary oxidation reactions occur, Isobutane such as the formationof tar or carbon, with lsobutnne decomposition of the sulfurlc ac1d tosulfur diox- 1 bute;1e ide and water. It is also known that under theseconditions excess or uncombined sulfuric acid Butadlene 4"75 increasesthe formation of polymers. n'Buta'ne 3o disadvantage of extract dilutionand steam strip- Z'butene' t g ping process is in the expense involvedin hanz'butene C15 dling, reconcentrating and reducing the carbon The 5carbon atom group of pentanes and pen- Co e of the 11013 diluteacidtenes is even more complex and the separation According to thepresent invention the secof these olefins from the associated saturatedolefins y be recovered from Olefinhydrocarbons byphysical means hasheretofore sulfuric acid solution without any substantial not beenaccomplished. loss due to polymerization and secondary oxida- There aremany chemical processes in which it tion and without the dilution orheating of the is a decided advantage to use a substantially pure acidextract. The following description will be olefin, unmixed with inertdiluents, such as sat- 4 related to normal butene separation but theprourated hydrocarbons. For example, in chemical cess described willalso have application to the reactions with the gaseous olefins in whichpresrecovery of other secondary olefins, such as prosure isadvantageous, the effective pressure is pylene, normal amylene, etc.normally the partial pressure of the reactive Sulfuric acid of about 70%to 90%, preferably olefin in the mixture. In such cases, substan- 83%,concentration is used to absorb the secontially pure olefins permit muchlower pressures dary olefins. This may be done at an elevated to beemployed and less gas to be compressed pressure in the liquid phase orat a lower presthan in the case of gas mixtures poor in reactive sure inthe gas phase. olefin. Also, in many cases the olefin reaction Whennormal butenes react with H2804, the may be reversible, the proportionof the desired resulting extract has been found experimentally productbeing dependent upon the concentrato contain some butene as such, someas secontion of the reactive olefin in the mixture. In dary butylalcohol, and some a mono-or dibutyl such cases, the dilution of theolefin with an sulfate. The extract is found to exert a considinertdiluent, such as a saturated hydrocarbon, 5 erable vapor pressure ofnormal butylene, de-

may so affect the yield of the desired reaction product as to render theprocess unprofitable. In addition, in cases where butenes are to besubjected to pyrolysis, as in butadiene manu-. facture, dilution withparaflins causes (1) loss of the paraflin, which is a valuable materialin Also, the

pending on the concentration of hydrocarbon and acid in the extract andon the temperature. Extracts of tertiary olefins, such as isobutylene,on the other hand, contain the olefin predominately as the tertiaryalcohol only and exert a negligible olefin vapor pressure.

The separation and recovery of secondary ole fins from strong sulfuricextracts is accomplished by the counter-current action of a saturatedhydrocarbon gas having at least 20 C. difference in the boiling pointfrom the secondary olefins such as propane or by extracting the olefinsfrom the strong olefin-sulfuric acid extract by the countercurrentaction of an inert liquid solvent such as pentane or hexane. It has beenfound that an extract of 83% sulfuric acid containing 1 mol of olefinper mol of sulfuric acid at 30 C. is in equilibrium with a liquidnaphtha containing 11% normal butene, while a similar extract containing0.2 mol of olefin per mol of sulfuric acid is in equilibrium with anaptha containing 1.2% normal butene. fin vapor pressures of these twoextracts are calculated to be 4.2 and 0.46 lb. per square inch,respectively. Therefore an 83% sulfuric acid extract containing 1 mol ofthe olefin per mol of th sulfuric acid can be stripped at 30 C. and atatmospheric pressure by passing it down a tower oountercurrently througha stream of gaseous propane and the gas leaving the top of the towershould contain approximately 25% normal butene and 75% propane. Thebutene is then recovered by fractionation and the propane recycled. Theextract leaving the bottom of the tower contains only 0.2 mol of olefinper mol of sulfuric acid and is recycled directly to the olefinabsorption equipment.

Alternately, a strong extract is treated countercurrently with liquidpentane and the liquid pentane leaving at the top of the extractiontower contains approximately 10% normal butene. The butene is recoveredby fractionation and the pentane recycled to the extraction tower. Whensome alkyl sulfate or alcohol is carried over mechanically or otherwiseby the pentane, it is readily separated as bottoms in the fractionatingtower and is recycled to the extraction step along with the pentane. Thelean acid extract from th extraction tower is recycled directly to theolefin absorption equipment.

The stripping or the extraction process requires a suitable length oftime as the reversion of alcohol or alkyl sulfate to olefins isrelatively slow. Since more time is generally allowed in extractionequipment than in stripping equipment, there are certain mechanicaladvantages in recovering the olefin by extraction. The extraction orstripping operation may be carried out at substantially atmosphericpressure and at temperatures below that at which substantialpolymerization of the olefins in the acid extract will take place,probably from to 60 C.

The invention will be more clearly understood on reading the followingdescription with reference to the accompanying drawing.

Numeral 1 designates the reactor into which is passed, at the upperpart, sulfuric acid of about 83% concentration b means of pipe 2, and amixture of hydrocarbons having four carbon atoms to the molecule andcontaining both butane and a secondary olefin is passed by means of pipe3 into a lower part of the reactor. 'An agitator Therefore thecorresponding ole- 4 is provided and cooling coil 5 to regulate thetemperature. The mixture of sulfuric acid and the hydrocarbons is thenpassed through pipe 8 into a settler l where the unabsorbed hydrocarbonsare removed by means of pipe 8 consisting mainly of butane. The sulfuricacid extract is removed from the settler 1 by means of pipe 9 and passedto the upper part of the liquid extraction tower ill. In the lower partof the liquid extraction tower Ill is passed a liquid parafiinichydrocarbon solvent, such as pentane, by means of pipe ll, which passesin countercurrent flow to the sulfuric acid in the tower. The sulfuricacid, with most of the olefins removed, is then recycled by means ofpipe l2 to the reactor l. The liquid pentane with the olefin solution isremoved from the extraction tower by means of pipe l3 and passed to afractionating tower M where the secondary olefins are distilled over topipe 15 and the liquid paraffinic hydrocarbon solvent is removed bymeans of pipe I l and recycled to extraction tower ill. Thefractionating tower i4 is provided with a condenser I? at the upper partand a heating coil [8 at the lower part.

I claim:

1. Improvements in the separation and concentration of a secondaryolefin from a hydrocarbon mixture containing the said secondary olefinwhich comprises contacting a hydrocarbon mixture containing a secondaryolefin with sulfuric acid of about 75%0% concentration, thereby forminga solution of the secondary olefin in said acid, extracting thesecondary olefin from said acid solution by means of a saturatedhydrocarbon compound, the said saturated hydrocarbon compound having atleast 20 C. difference in boiling point from the secondary olefin,capable of dissolving the secondary olefin and separable from the saidsecondary olefin by fractionation.

2. Improvements in the separation and concentration of a secondaryolefin from a hydrocarbon mixture containing the said secondary olefinwhich comprises contacting a hydrocarbon mixture containing a secondaryolefin with sulfuric acid of about 75%-90% concentration, therebyforming a solution of the secondary olefin in said acid, extracting thesecondary olefin from said acid solution by means of a saturatedhydrocarbon compound in the liquid phase, the said saturated hydrocarboncompound having at least 20 (Indifference in boiling point from thesecondary olefin, capable of dissolving the secondary olefin andseparable from the said secondary olefin by fractionation.

3. Improvements in the separation and concentration of a secondaryolefin from a hydrocarbon mixture containing the said secondary olefinwhich comprises contacting a hydrocarbon mixture containing a secondaryolefin with sulfuric acid of about '75%90% concentration, therebyforming a solution of the secondary olefin in said acid, extracting thesecondary olefin from said acid solution by means of a saturatedhydrocarbon compound in the vapor phase, the said saturated hydrocarboncompound having at least 20 C. difference in boiling point from thesecondary olefin, capable of dissolving the secondary olefin andseparable from the said secondary olefin by fractionation.

HAROLD W. SCHEELINE.

